New bumper starts from Rs. 3500
It can be repaired even if its broken into pieces.
Paint charges depends on the quality you want, from 1500 to 3000.
It will take about 4 liters. You can drain about 70% coolant from radiator and need to open a bolt next to oil filter to take out coolant from the block.
It will not fix decreasing water issue, you need to find the root cause.
Either gasket or one of the hoses has a small leak maybe size of pinhole.
When you open radiator cap, is there any pressure in radiator or reservoir????